It was said at Blizzcon that the non auto attack wasn't set in stone and that they are very split about it. There are issues with the non auto attack such as not being able to finish a mob off that has little hp remaining without wasting resources. I got to play the pre-alpha for a bit and it very much reminded me of ff14 button mashing of 111111111. While it wasn't terrible i missed the option of auto attacking just for ease of killing. Maybe they will change it, maybe they will axe it, who knows.